A bumper installed at front and back of a vehicle is an impact absorbing device protecting the vehicle and passengers in some degrees by primarily absorbing impact when the vehicle collides. These bumpers comprise a bumper back beam fastened on a body frame of a vehicle through a bumper stay, an impact absorbing foam fastened on the front side of the bumper back beam, and a bumper cover fastened on a bumper with the impact absorbing foam in between.
There are a variety of bumper back beams, such as a type illustrated in FIG. 1.
FIG. 1 is a drawing illustrating a prior disassembled bumper back beam.
As illustrated, a prior back beam comprises a main body (11) fastened inside a bumper cover (not illustrated), and a stay (12) to connect the main body to a frame of a vehicle.
The main body (11) is formed by a fiber composite reinforcing material, and cross sectional shape of line A-A assumes a form of an open shape.
For example, it is what has a “U” similar shaped cross section. The reason for forming main bodies with fiber composite reinforcing materials as described above is to reduce the weight of vehicles.
Prior back beams formed with fiber composite reinforcing materials are generally made by combining glass fiber with synthetic resin and physical characteristics such as strength, stiffness, and fracture elongation depends on the glass fiber. That is, strength and stiffness of a back beam using fiber composite reinforcing materials greatly increases compared to back beam made of only synthetic resin, but elongation sharply decreases. Due to the described reason, when impact load applied to a fiber composite reinforcing material back beam is not high, absorbing impact energy of back beams are effective due to influence from high strength and stiffness, but there are disadvantages that efficiency of impact energy absorption may sharply decrease because it easily cracks because elongation is rather poor at high impact loads.